So I need to loop through a few files and compare specific columns. The most basic way of doing this is through nested foreach loops, and my current script is running that fine, it just will take a long time. I was wondering if there were any quicker substitutes for a nested foreach statement, as later I was going to do this again, but with 3 files to build a new one. The main issue is that each of these files is >2million lines, so any suggestion on improving the speed would be greatly appreciated.